1. Field of the Invention
This invention relates to a transistor amplifier circuit and more particularly to a loud-speaker output circuit capable of producing audio signals with a high degree of fidelity.
2. Description of the Prior Art
A audio frequency amplifier for amplifying sound signals representing, for example, voices or musical tones is demanded to carry out said amplification without distortion. The high fidelity amplification of the audio frequency amplifier is supposedly obstructed by the amplitude distortion phase distortion or inter modulation distortion of sound signals resulting from the nonlinear characteristic of an active element such as a vacuum tube or transistor.
Hitherto, various attempts have been made to minimize said nonlinear characteristic. However, any attempt made to date failed to attain the satisfactorily fidelity amplification of the audio frequency amplifier. Particularly, the transistor amplifier was generally found to carry out less fidelity amplification than the vacuum tube amplifier. Though several explanations have been proposed regarding the different degrees of fidelity in amplification between the vacuum tube and transistor amplifier, yet the factor has not been clearly defined. The above-mentioned case is supposed to arise from the fact that the transistor has a lower input impedance than the vacuum tube. Therefore, an amplifier using a field effect transistor having a high input impedance was put to practical application for trial. Yet, this type of amplifier failed to be fully improved in the fidelity of amplification.